leetcode 152. Maximum Product Subarray

Given an integer array nums, find the contiguous subarray within an array (containing at least one number) which has the largest product.

Example 1:

Input: [2,3,-2,4]
Output: 6
Explanation: [2,3] has the largest product 6.
Example 2:

Input: [-2,0,-1]
Output: 0
Explanation: The result cannot be 2, because [-2,-1] is not a subarray.

题意：求最大的连乘。

思路：维护到当前位置的最大值和最小值。dp[i][0]表示最小值，dp[i][1]表示最大值。

class Solution {
public:
    int maxProduct(vector<int>& nums) {
        int n = nums.size();
        vector<vector<int> > dp(n, vector<int>(2));
        int ans = INT_MIN;
        if (n == 1) return nums[0];
        for (int i = 0; i < nums.size(); ++i) {
            if (i == 0) {
                dp[i][1] = nums[i];
                dp[i][0] = nums[i];
            } else {
                if (nums[i] > 0) {
                    dp[i][1] = max(dp[i-1][1]*nums[i],nums[i]);
                    dp[i][0] = min(dp[i-1][0]*nums[i],nums[i]);
                }
                else {
                    dp[i][1] = max(dp[i-1][0]*nums[i], nums[i]);
                    dp[i][0] = min(dp[i-1][1]*nums[i], nums[i]);
                }
            }
            ans = max(max(dp[i][0],dp[i][1]), ans);
        }
        return ans;
    }
};

这个代码还可以优化，比如不用数组，同时也不用判断nums[i]是大于0还是小于0